A runoff that will be decided more by the whims of Mother Nature than the dictates of man has river watchers holding their collective breaths.

On the heels of a seven-year drought and a winter of record snowfalls that caused high-country roofs to collapse, will this year’s spring runoff in the Gunnison Basin overwhelm the three Aspinall Unit dams and crash unhindered through the Black Canyon of the Gunnison River?

Or will it disappear without a whimper, as did the foretold but never realized runoff of 2005?

The art of forecasting a spring melt isn’t done by the witches of “Macbeth,” peering intently into a boiling cauldron, but with all due respect to the Bureau of Reclamation, that technique might be as good as any.

Hydrologists at the Grand Junction office of the Bureau of Reclamation, aided by constant monitoring of high-country snowpacks and years of accumulated data, make a series of runoff forecasts starting each winter and going into early summer.

Snowpack depths and water content are key to what might happen in the future, although the actual downriver flow depends on other factors, including how fast the snow melts and how much of that water the ground inhales before it reaches the stream.

Early April indications are that this year’s runoff will be the highest in many years. The most recent forecast calls for 1.06 million acre-feet of water to flow into Blue Mesa Reservoir this spring compared to 460,000 acre-feet forecast on April 1 last year.

But if Mother Nature throws a week of unseasonably high temperatures at the high country, as she did in 1984, the entire snowpack might rush down in the blink of an eye. Or, conversely, an unseasonably cool spring could slow or even delay the runoff.

Who cares about a high runoff?

Anglers care because it’s been at least a decade since high flows have swept through the Black Canyon and the Gunnison Gorge, and the ensuing years have seen an unsightly buildup of sediment in the river.

The Colorado Division of Wildlife cares because high flows at the wrong time could seriously affect the world-class trout fishery the agency is fostering in the river.

The U.S. Fish and Wildlife Service cares because timely high flows are critical for spawning and reproduction of native threatened and endangered fish downstream of Delta.

And, of course, residents of Delta and other low-lying areas care because unusually high flows could mean flooding troubles.

WHERE IT ALL STARTS

The three Aspinall Unit dams — Blue Mesa, Morrow Point and Crystal — were authorized by the 1956 Colorado River Storage Project Act. Under that act, the three dams (and the other project units, including Flaming Gorge and Navajo dams) were built for flood control, irrigation and generating hydropower.

Power generation is mandated by the act, which says, “The Secretary (of the Interior) must operate the authorized hydroelectric power plants and transmission lines ... to produce the greatest practicable amount of power and energy ...” The revenues from the generation pay for the dams’ construction.

Blue Mesa and Morrow Point are peak-power dams, while Crystal generates constant power. When air conditioners turn on across the West and drain the system, the generators at Blue Mesa and Morrow Point whir into action. Water rushes into the hydroturbines, increasing the river flow downstream of the dams. Those higher flows are moderated by Crystal Dam before they reach the river downstream.

The energy is sold on the Western power grid by the Western Area Power Administration, an agency of the Department of Energy. The agency is perhaps the major player in how the dams are operated, since it’s the agency’s job to make sure any stored water goes first to power generation.

The Bureau of Reclamation tries to maintain water for power generation, which means year-round planning on how and where water will be stored. That also means the bureau must make sure there is room each spring in Blue Mesa for runoff, which usually means deciding how much water to release all winter in anticipation of runoff filling the reservoir in the spring.

A similar water year, based on snow monitoring reports, was forecast in 2005. The Bureau pulled water out of Blue Mesa, anticipating a runoff that never came.

“That was a real heartbreaker,” said Dan Crabtree, lead hydrologist for the Bureau’s Grand Junction office.

This year, with forecasts calling for high runoff, the Gunnison is running higher than it has in nearly a decade. Friday, the gauge just below Crystal Dam was at 2,930 cubic feet per second, compared to one-third or less of that at this time in recent years.

WHAT IT MEANS

Higher flows affect the fishing, but that’s not the bureau’s worry. Recreation is mentioned only as a mitigation for losses incurred by the CRSP projects’ development.

The Bureau of Reclamation is not responsible for downstream recreation, in this case the fishery in the Gunnison River.

That’s an important point, because it’s recreational anglers, in particular Trout Unlimited, who are eyeballing the heavy snowpack and saying this is the year the bureau should release extra-high flows to benefit the Gunnison River.

“Trout Unlimited’s hope is that, under the present snowpack conditions, we would see a real good flush this year,” said Drew Peternell, director of the Colorado Water Project with Colorado Trout Unlimited. “We think something around 6,000 (cubic feet per second) or maybe more would be adequate.”

Adequate, that is, to move out some of the sediment that’s settled in the Gunnison River. Much of the sediment apparently came when Crystal Reservoir was drained in 1999 for some maintenance work on the trash racks.

Even though the Bureau of Reclamation immediately pushed 5,000 cfs through the canyon, the sediment still clogs parts of the river.

Some Trout Unlimited members have been pressuring the bureau into committing to a high flush flow. In an e-mail Peternell sent to several local Trout Unlimited members and to Bart Miller, an attorney with Western Water Resources, Peternell responded to an earlier inquiry by saying, “I do not think we have a cause of action to force the BOR to make larger releases this year.”

As the runoff forecasts grow, the Bureau of Reclamation has bumped up releases into the Gunnison, a move that Trout Unlimited questions.

“Instead of doing that, we would prefer they would have held back some water this winter to provide a big flush sometime late in May,” Peternell said.

Many anglers are concerned about how high water might affect the river’s renowned Pteronarcys stonefly (aka the salmonfly) hatch, which historically happens in mid-June. But Division of Wildlife aquatics biologist Dan Kowalski said high water affects anglers more than salmonflies.

“The stoneflies naturally evolved with high flows,” he said. “The Gunnison is unique (among Western rivers) in that it’s a tailwater where you can fish during the normal runoff. High flows only affect the ability of people to fish the hatch.”

So, the still-unanswered question is, what will the Bureau of Reclamation release this year?

Coll Stanton, a veteran hydrologist with the local Bureau of Reclamation office, said it’s possible, if the forecast prediction holds true, there could be an extra 30,000 to 100,000 acre-feet of water flowing into Blue Mesa, which at its maximum holds 829,500 acre-feet.

That means, if all goes as predicted (and remember those witches trying to influence Macbeth’s fate), that much water would top the dams and flow downstream. Not at once, hopefully.

“Even if we go to full bypass, if the model we have holds up, we probably will have some spill, anyway,” Stanton said.

But it’s not clear what effect the high flows, even the flush flows, will have on the fishery. Kowalski said flush flows “are a hot-button topic” this spring.

Even though the buildup of sediment is easily seen, its effects aren’t so easy to determine.

“One impact that’s been hypothesized is the sediment settles in trout redds (nests) and causes a decrease in reproductive success,” Kowalski said. “But that hasn’t happened, at least as far as brown trout reproduction (in the Gunnison River) is concerned.”

He said brown trout reproduction the last two years has gone “through the roof,” and “two of the highest brown trout year-classes have been in the last two years.”

Another concern voiced by Trout Unlimited is the effect the sediment has on the aquatic bugs trout eat. That, too, isn’t clear, Kowalski said.

“We don’t have any long-term bug data, so I can’t speak to what large impact sediment might have, but what I can say is there hasn’t been any effect on trout body condition yet,” he said.

If the sediment had affected the bug life, fish conditions would decline, but Kowalski said Gunnison River trout are as least as plump as fish in comparable rivers.

Kowalski noted the sediment appears to have settled in the slower pools and not the oxygen-filled riffles preferred by trout.

“Flushing flows (and sediment transport) are important for the river, but we don’t have any biological data that show the fish population (in the Gunnison) has suffered from the lack of flush flows,” Kowalski said.

While that might not be popular with Trout Unlimited, “it’s based on the best biological data we have,” Kowalski said.

Also, the sediment appears to have settled in the slower pools, areas considered poor trout habitat anyway. While the sediment is good habitat for the tubifex worm that transmits whirling disease, there isn’t enough water in the entire Gunnison Basin to get rid of whirling disease in the Gunnison, Kowalski.

He’s withholding any request for flows until he hears the bureau’s latest forecast, which will be released at the Aspinall Operations meeting Thursday in Grand Junction. The meeting takes place at 1 p.m. in the Bureau of Reclamation’s Grand Junction office, 2764 Compass Drive, Suite 106.

“From a biological standpoint, there’s no need for large peak flows,” Kowalski said. “Moderate peaks are plenty to sustain the trout fishery and not threaten it. A peak flow of 4,000 to 6,000 cfs is plenty. Bigger flows are more beneficial to the native fish downstream.

“For the trout fishery’s benefit, you don’t need flows over 6,000, ever.”

Timing of peak flows also is critical. Trout fry are most susceptible the first month after they emerge from the nest. Rainbow trout young emerge late April to early July, so a high flow in that period would wash them away.

Brown trout fry emerge in early spring, and this year’s class was hurt by extraordinarily low flows in March, when the Bureau of Reclamation did maintenance on Crystal and Blue Mesa dams. Most of this year’s fry were stranded by low water before they emerged from the nest, Kowalski said.

“Right now, for the 2008 spring operations, we don’t have anything written in our guidelines” regarding river flows in the Black Canyon, said Chuck Petty of the Park Service water rights office.

So everyone waits. There will be some immediate response this week when the Bureau of Reclamation releases its new forecast, but most of the answers will come later this spring when Mother Nature proves or disproves the soothsayers’ ability.

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E-mail Dave Buchanan at dbuchanan@gjds.com.

KNOW YOUR FLOWS
There are peak flows and there are flush flows.
Every spring you see peak flows, the river’s profile naturally rising and falling like a Bell curve. The Bureau of Reclamation tries to manage storage (through early releases, increased power generation and the dams’ bypass tubes) so runoff flows don’t overwhelm the dam. Flows that go over the top are considered “uncontrolled flows” and mean the water goes unused for power. Uncontrolled flows make the Western Area Power Administration cringe.
Flush flows, on the other hand, are understood to be water releases in addition to the normal peak flows and are wanted to provide cleansing flows downstream. Flush flows can be a prolonging of the peak flow or a release of stored water in addition to that released during the peak times.THE ISSUE
With the Gunnison Basin likely facing its heaviest spring runoff in more than a decade, there is great interest in how much of that water will make it into the Gunnison River. Anglers, conservationists and fisheries managers are keenly interested in how the Bureau of Reclamation, which operates the three Aspinall Unit dams, will control the speed and amount of flows released through the dam system.
This story looks at the concerns and how the bureau decides when and how much of the water it will release.